A theoretical study on the effects of intramolecular and intermolecular interactions on excited state properties of two NIR-TADF combined with AIE molecules.

In this work, we systematically study the photo physical properties for NIR-AIE-TADF molecules in toluene solvent, film and crystal by PCM and QM/MM method, respectively. First, the molecular luminescence was red-shifted by about 100 nm, when –CH3 in the molecule is replaced by –OCH3, which may be due to the increased vibrational intensity of the molecule, resulting in energy dissipation. Second, the vibrations were effectively suppressed in the solid state for both TBSMCN and O-TBSMCN molecules, which is the reason for the AIE of the molecules. Third, the molecules have a small △ES1-T1 in the solvent with TADF properties, and their △ES1-T1 is reduced and SOC is increased in the solid state, which is more favorable for the RISC. Fourth, by analyzing the nature of the transitions in the dimers in the film structure we find that O-TBSMCN molecule undergoes intermolecular charge transfer, which may be one of the reasons for its reduced film efficiency. [Display omitted] • The inhibition of vibration in the aggregated state is the main reason for AIE. • A smaller △E S1-T1 and a larger SOC in aggregate state, it is favorable for RISC. • The O-TBSMCN molecule undergoes intermolecular CT, which lower its film efficiency. TADF emitters with both high exciton utilization and luminescence efficiency show promising applications in OLEDs, especially it with AIE characteristics. However, theoretical studies on emitters with amorphous structure with the consideration of the solid-state effect are limited. In this work, a multi-scale simulation is performed to study the reported compounds TBSMCN and O-TBSMCN, which both possess distinct features of NIR-AIE-TADF. The packing modes of the molecules in film and crystal are obtained by molecular dynamics simulations (MD) and experiments, and then the photo physical properties are studied by using the QM/MM method. The results show that geometrical changes between the ground state (S 0) and the first singlet excited state (S 1) are restricted in aggregate state. Thus, the non-radiative energy consumption process is hindered, this indicates the AIE mechanisms. Second, the molecules exhibit a smaller △E S1-T1 and a more significant SOC in aggregate state, which is more favorable for the RISC. Finally, by analyzing the NTO of the dimers in the film, the O-TBSMCN molecule undergoes intermolecular charge transfer, which may be one of the reasons for the significant reduction in its film efficiency. Our calculations could help one to better understand the NIR-AIE-TADF mechanism from a theoretical perspective. [ABSTRACT FROM AUTHOR]